Plans to ban most conventional cars from the roads within the next 30 years could feature in the Liberal Democrats' offering to voters at the next general election.
But the proposal from Nick Clegg's party to only allow ultra-low carbon vehicles on British roads by 2040, other than for freight purposes, will first have to be approved at next month's Lib Dem conference.
If the conference votes in favour of the plan it will become party policy and may feature in the party's manifesto for the 2015 General Election, a Lib Dem spokesman said.
The proposal was unveiled as Society of Motor Manufacturers and Traders figures showed that car sales, a key indicator of the health of the British economy, had risen 12.7% on last year.
The spokesman said: "The way that our party policy is decided is that conference has the vote. (If they vote in favour) that will become party policy. It is a target for 2040, it is part of a wider strategy, it is something that we are committed to doing in a wider sense.
"It could be in the manifesto but conference will have a big say, we would not want to pre-empt the vote. If conference votes for it, it becomes party policy."
The idea was revealed in the agenda for the Lib Dems' mid-September conference in Glasgow alongside plans to allow councils to introduce congestion charges.
The conference will vote on a Lib Dem policy paper entitled Green Growth And Green Jobs - Transition To A Zero Carbon Britain, which contains the plans to decarbonise the transport sector by "specifying that, by 2040, only ultra-low carbon vehicles will be permitted on UK roads for non-freight purposes, and preparing for the introduction of a revenue-neutral system of road pricing and supporting local authorities introducing road pricing in congested areas."
The AA warned that motorists would be hit with a "double whammy" if the plans ever became law.
Paul Watters, head of policy at the AA, said: "You can't have an absolute date for saying these cars shouldn't be on the road. It does seem wrong to consign petrol and diesel cars to that age of history. The sting in the tail is that they are also talking about road pricing, so not only are drivers being told they can't drive petrol or diesel, but they are being told there will be road pricing as well, so it's a double whammy."